Numerical simulation of damage of masonry and masonry infilled RC frame structures to blast ground motions

This paper performs the 3-dimensional dynamic response and damage analysis of masonry structures and masonry infilled RC frame structures to blast induced ground motions. A two-storey masonry structure and a two-storey masonry infilled RC frame as well as a six-storey RC frame filled with masonry walls are used as examples in the study. The previously developed 2-dimensional continuum material damage models including the orthotropic elastic model, strength envelope and damage threshold of masonry, are extended to 3-dimension and applied to masonry. The material damage models developed for reinforced concrete structure are also extend to 3-dimension to model RC damage to high-frequency ground excitations. Structural damage to different ground excitations is simulated. The ductility ratios of the masonry structure and the inter-storey drift of the masonry infilled RC frames are also calculated for comparison. Numerical result shows that a structure under high frequency ground motions suffers brittle failure and damage is governed by the force-stress rather than the inter-story displacement or ductility. The present results further verify the conclusions drawn in previous studies based on a 2-dimensional numerical model and on laboratory tests, i.e. 9 structural response and damage to high-frequency blast ground motions are dominated by high vibration modes. Therefore displacement response based criteria such as ductility ratio and inter-storey drift as commonly used in earthquake engineering for assessing structural performances cannot be directly applied to structures to blast ground motions. The present numerical results are also compared with those obtained from the 2-dimentional analyses. Discussions on the adequacy of the code as well as empirical allowable blast ground motion levels to structures are also made.